Satanic comma: The difference between 665 fifths and 359 octaves, less than 1/10 of a cent, around 1/15878 of an octave. Marc sees this as a possible musical insight into the cryptic quote from the Book of Revelation, citing “the beast” as a man-made number which only someone with understanding could calculate: “It stands to reason that if the 665th turn of the cycle of fifths, modulo octave, is so close to unison as to be imperceptible, and deceive you as unity, then similarly the 666th turn would be able to deceive you as being a true fifth. (coined 1990, as a parody on the name of the syntonic comma.)